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Secrets of the Northern Lights

Scientist sheds light on the hows and whys of this atmospheric wonder

Keith Vandervort
Posted 1/31/15

ELY – The night sky in Northern Minnesota can be filled with the eerie, mysterious ribbons of light known as the aurora borealis. Lovely to look at and a challenge to photograph, the Northern …

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Secrets of the Northern Lights

Scientist sheds light on the hows and whys of this atmospheric wonder

Posted

ELY – The night sky in Northern Minnesota can be filled with the eerie, mysterious ribbons of light known as the aurora borealis. Lovely to look at and a challenge to photograph, the Northern Lights are produced as part of the relationship between the earth and the sun.

Dan Miller, a science officer with the National Weather Service office in Duluth, visited the Wolf Center in Ely last weekend and explained the basic science of solar physics and magnetism that produces the magical light show so many up north take for granted.

His lecture was part of a weekend photography workshop hosted by popular Northern Lights photographer Heidi Pinkerton of Babbitt.

“We have a hard time predicting space weather and forecasting the Northern Lights,” he said. “We have enough trouble with terrestrial weather, as you know.”

He explained that forecasting space weather is so difficult because of the distance of some 93 million miles between observing what happens on the sun and taking measurements of the solar wind using one satellite orbiting the earth.

“The aurora that we see is basically an emission of light from energized or excited nitrogen and oxygen hundreds of miles above the surface of the earth,” Miller said. “This is caused by a stream of charged particles that travel from the sun and interacts with the gases in our atmosphere and the magnetic field around our planet.”

The aurora borealis also occurs in the southern hemisphere and are called, of course, the Southern Lights, or aurora australis.

Miller explained that the describing of the phenomenon of the aurora borealis goes way back in human culture – as early as 5,000 years ago in China and also to the Babylonians.

He showed a photograph of a Cro-Magnum period cave painting of the Northern Lights from as far back as 30,000 BC. “Most native and aboriginal cultures that lived in the northern latitudes of North American and Asia and also in Australia did have cultural beliefs that they held about the aurora from wonder to fear to (acts of) gods and other things,” he said.

“The true scientific discovery as we define science started with a Northern Lights event that was visible in Europe on Sept 12, 1621, by one of the usual scientific suspects, Galileo, who helped coin the term aurora borealis, which comes from a combination of the Roman god of dawn, aurora and the Greek name for the north wind, which is borealis,” he said.

Space Weather

The aurora borealis occur 60 to 300 miles above the earth, Miller said. “Space weather encompasses many other things besides the Northern Lights,” he said. “It impacts satellites, GPS. air travel, power grids, pipeline operations.”

“With how interconnected our planet is with technology, you can imagine what would happen if we had a severe solar event and how it could impact our entire planet. Terrestrial weather is local and space weather is global. Its really is a matter of when, not if.”

He said all space weather, as it pertains to earth, starts with the sun. The sun emits several kinds of waves of energy across the spectrum, from radio and microwaves visible light, to x-rays and ultraviolet waves.

The sun rotates much like the earth, however, the sun does not rotate like a solid body. The sun rotates faster at the equator than at the poles. “The sun has a magnetic field around it, much like the earth, but on the sun the magnetic field gets stretched and pulled because of the different rotation speeds,” Miller said.

Plasma will eject from the sun as a result of the constantly fluctuating magnetic forces. These “coronal mass ejections” will sometimes head toward earth and the particles will interact with the earth’s magnetic field. “Magnetism is a much more powerful force than gravity and electricity,” he said. Magnetic field strength, speed and orientation to the earth determine when and how much of these charged particles will make their way toward earth, and interact with this planet’s magnetic field in such a way as to make the charged gases visible to those people looking at the night sky.

What about all those colors?

Essentially, magnetically charged oxygen particles will appear to glow more red at high elevations, green at lower levels. Magnetically-charged nitrogen particles will appear to glow more blue and purple. Miller said a pale green color is the most common color of aurora borealis visible to the human eye.

“Many factors can influence the color of the Northern Lights that we see,” he said. Those factors include the orientation of the viewer to charged particles. “They can be directly overhead or low on the horizon,” he said. The time of day, time of year, phase of the moon and what the eye sees versus what a digital camera will record will all contribute to the color variations.

The fact that Northern Lights are usually more visible during the winter months is due to the simple fact that the nights are longer in the winter and the charged particles are visible for a longer period of time.

So many of the photographic images of the aurora borealis hanging in local galleries may not be exactly what the photographer saw while recording the image. Altering the white balance setting and post processing or manipulating the image using a computer program can drastically change appearance of the image, he said.

“The camera is the camera. It is sensitive to all wavelengths of light, during the day and at night. The human eye is not. One of the first things that happens at night is we lose our color perception,” he said. “Most of the time you see a milky, white glow.”

He gave some advice to getting the most out of capturing images of the Northern Lights. “Be diligent about it,” he said. “Learn how to interpret the real-time data (of solar events), and be flexible. That is the most important thing - being able to stay up all night or part of the night when something gets going.”